.338 ARC AR-15 Upper Assemblies

High-Energy Subsonic and Supersonic .338 ARC Builds

Moriarti Armaments builds complete AR-15 .338 ARC upper assemblies in Miami, in 4.5", 7.5", 10.5", 12.5" and 16" barrel lengths with M-LOK handguards. .338 ARC is Hornady's .338-caliber cartridge for the AR-15: heavy subsonic bullets run quietly through a suppressor, and supersonic loads add energy for hunting, all on a standard-size AR-15 lower.

The short uppers are built as compact suppressor hosts for AR pistol and SBR builds; the 16" upper fits a standard rifle lower without short-barrel paperwork. Barrels are nitride-finished 4150 steel.

Can I use a 6.5 Grendel bolt with a .338 ARC upper?

Yes. .338 ARC uses a 6.5 Grendel Type II bolt, not a standard 5.56 bolt. Only the barrel and caliber-specific parts change. Always verify compatibility with your specific upper receiver and manufacturer specifications before assembly.

More Questions

Which barrel length should I choose for .338 ARC?

Short 4.5" to 10.5" uppers are built for compact, suppressed builds with subsonic ammo. 12.5" and 16" uppers add velocity for supersonic loads and hunting.

Is .338 ARC good for suppressed shooting?

Yes. It was designed to run heavy subsonic bullets quietly through a suppressor while still offering supersonic loads for longer range.

Are a BCG and charging handle included?

No. Our .338 ARC uppers ship without them; add a 6.5 Grendel Type II bolt carrier group and a standard AR-15 charging handle.

What magazines does .338 ARC use?

6.5 Grendel / ARC-family magazines, or magazines made for .338 ARC.

Related: .338 ARC barrels · .338 ARC build kits · .338 ARC magazines · .338 ARC pistols · all AR-15 upper assemblies